1. Field of the Invention
The present invention relates generally to a charger for use in an image forming apparatus such as, for example, a copier or a printer and, more particularly, to a contact charger for electrostatically charging a photosensitive member by bringing a charging member into contact with such photosensitive member.
2. Description of the Related Art
In an electrophotographic image forming apparatus such as a copier, a printer or the like, image formation is performed by charging a photosensitive member with the use of a charger; forming an electrostatic latent image on a charged region of the photosensitive member by subsequent exposure to imagewise rays of light; developing the electrostatic latent image into a visible powder image; transferring the visible powder image onto a transfer material; and fixing the transferred visible powder image.
Various types of chargers are known and are broadly classified into corona chargers, wherein corona discharge is utilized, and contact chargers wherein the surface of the photosensitive member is brought into contact with a charging member such as, for example, a charging brush, a charging roller, a charging blade or a rotatably arranged endless charging belt.
The corona chargers have the advantage of providing a stable charging process, but have the disadvantage of producing a large amount of ozone, which tends to cause deterioration of the photosensitive member and to adversely affect human bodies. Because of this, the contact chargers are noticed which produce considerably less ozone than the corona chargers.
The contact chargers, however, have some disadvantages. The chargers employing the charging brush have the disadvantage of requiring much time to make the brush. The chargers employing the charging roller have a complicated structure because they require means for driving the roller. In addition, because the roller is left in contact with a photosensitive drum even when the image forming apparatus is at a standstill, creep deformation strains remain on the contact portion, thus resulting in insufficient charging. The chargers employing the endless belt have the disadvantage of increasing the size of the image forming apparatus and requiring a complicated structure for driving the belt.